Effect of pressure on electrical conductivities of fused alkali metal halides and silver halides

Abstract

The electrical conductivities of the following fused salts were measured at temperatures up to 860°C and over a pressure range 1–1000 bar: the chlorides, bromides and iodides of the five alkali metals; silver chloride, silver bromide. The volumes ΔV_Λ=–RT(∂ ln Λ/∂P)_T were calculated to be independent of temperature for each salt. ΔV_Λ was zero for the lithium halides, and increased as the ions were changed in the sequences Li⁺→Cs⁺ or Cl^–→I^–. The ΔV_Λ values were used to find the temperature dependence of conductivity at constant density from that at constant pressure. The results are not consistent with the free volume theory, or with the hole theory of Bockris and Hooper. However, the observed trends are in qualitative accord with the Rice–Allnatt statistical theory of transport in liquids. This theory was used to calculate the conductivity of fused potassium chloride and its pressure and temperature dependence, using ionic pair correlation functions obtained in a computer-simulated ionic dynamics experiment. The results are in moderate agreement with experiment.